According to the prior art, especially for motor vehicles, automatic transmissions comprise planetary gear sets shifted by means of frictional and shifting elements like clutches and brakes and are usually connected with a starting element such as a hydrodynamic torque converter or a fluid clutch liable to a slip effect and optionally provided with a lock-up clutch.
Such a transmission results from EP 0 434 525 A1. Essentially, it comprises one drive shaft and one driven shaft disposed in parallel, one double planetary gear set located concentrically to the drive shaft and five shifting elements in the form of three clutches and two brakes, the optional locking of which by pairs determines different gear ratios between the drive shaft and the driven shaft. This transmission has one front-mounted gear set and two power paths so that by selective engagement by pairs of the five shifting elements six forward gears are obtained.
In the first power path, two clutches are needed here to transmit the torque from the front-mounted gear set to two elements of the double planetary gear set. These are situated in power flow direction essentially behind the front-mounted gear set toward the double planetary gear set. In the second power path, one other clutch is provided which detachably connects them with another element of the double planetary gear set. The clutches are here disposed so that the inner disc carrier forms the output.
From the publication U.S. Pat. No. 6,139,463 a compact multiple gear transmission in planetary design is further known, especially for a motor vehicle, which has two planetary gear sets and one front-mounted gear set, the same as three clutches and two brakes. In this known multiple gear transmission, two clutches C-1 and C-3 are provided in a first power path for transmitting the torque from the front-mounted gear set to the two planetary gear sets. The outer disc carrier, the cylinder or piston and the pressure-compensation sides of the clutch C-3 are here respectively connected with one first brake B-1. Besides, the inner disc carrier of the third clutch C-3 is connected with the cylinder or piston and pressure-compensation sides of the first clutch C-1, the inner disc carrier of the first clutch C-1 being located on the output side and connected with a sun gear of the third planetary gear set.
From the Applicant's DE 199 49 507 A1 is also known a multiple gear transmission where two non-shiftable front-mounted gear sets on the drive shaft are provided which produce two rotational speeds on the output side which, together with the rotational speeds of the drive shaft, can optionally be shifted to the shiftable double planetary gear set acting upon the driven shaft by selective closing of the shifting elements used in a manner, such that to change from one gear to the respective next following higher or lower gear, only one of the two precisely actuated shifting elements has to be engaged or disengaged.
From DE 199 12 480 A1 one automatically shiftable motor vehicle transmission is also known, having three one-spider planetary gear sets, the same as three brakes and two clutches, for shifting six forward gears and one reverse gear and having one drive shaft, the same as one driven shaft. The automatically shiftable motor vehicle transmission is designed so that the drive shaft is directly connected with the sun gear of the second planetary gear set and that the drive shaft can be connected via the first clutch with the sun gear of the first planetary gear set and/or via the second clutch with the spider of the first planetary gear set. Additionally or alternatively, the sun gear of the first planetary gear set can be connected via the first brake with the housing of the transmission and/or the spider of the first planetary gear set via the second brake with the housing and/or the sun gear of the third planetary gear set via the third brake with the housing.
From DE 102 13 820 A1 a multiple gear automatic transmission is further known comprising one first input lane T1 of a first reduction ratio; one input lane T2 having a higher reduction ratio than said input lane T1; one planetary gear set with four elements which are one first element, one second element, one third element and one fourth element in the sequence of elements in a rotational speed diagram; one clutch C2 which transmits a rotation from the input lane T2 to the first element S3; one clutch C-1 which transmits a rotation from the input lane T2 to the fourth element S2; one clutch C-4 which transmits a rotation from the input lane T1 to the first element; one clutch C-3 which transmits the rotation from the input lane T1 to the second element C3; one brake B-1 which produces the engagement of the fourth element; one brake B-2 which produces the engagement of the second element; and one output element which is coupled with the third element R3.
Within the scope of the Applicant's DE 101 15 983 A1 a multiple gear transmission is described, having one drive shaft connected with a front-mounted set, one driven shaft connected with a rear-mounted shifting set and with a maximum of seven shifting elements by optional shifting of which at least seven forward gears can be shifted without group shift. The front-mounted set is formed by one front-mounted planetary set or at most two non-shiftable front-mounted planetary gear sets coupled with the first front-mounted planetary gear set wherein the rear-mounted set is designed as two-spider four-shaft transmission with two shiftable rear-mounted planetary gear sets and has four free shafts. The first free shaft of this two-spider four-shaft transmission is connected with the first shifting element, the second free shaft with the second and third shifting elements, the third free shaft with the fourth and fifth shifting elements and the fourth free shaft with the driven shaft. For a multiple gear transmission having a total of six shifting elements, it is inventively proposed to connect the third free shaft or the first free shaft of the rear-mounted set additionally with a sixth shifting element. For a multiple gear transmission having a total of seven shifting elements, it is inventively additionally proposed to connect the third free shaft with a sixth shifting element (D′) and the first free shaft with a seventh shifting element.
Within the scope of the Applicant's DE 101 15 987, a multiple gear transmission has also been described having at least seven gears. The transmission comprises, together with the drive shaft and the driven shaft, one non-shiftable front-mounted gear set and one shiftable rear-mounted gear set in the form of a two-spider four-shaft transmission. The front-mounted gear set consists of one first planetary gear set which, together with the input rotational speed of the drive shaft, offers a second rotational speed which can optionally be shifted to a rear-mounted gear set. The rear-mounted gear set is comprised of two shiftable planetary gear sets which, with the six shifting elements, can engage at least seven gears, two power paths being formed. At the same time, group shifts are always advantageously prevented during each shifting operation. One 9-gear multiple gear transmission has also been disclosed in DE 29 36 969; it comprises eight shifting elements and four gear sets.
Automatically shiftable vehicle transmissions in planetary design have often been described already in the prior art and can be an object of constant further development and improvement. Thus the transmissions must have sufficient number of forward gears, the same as one reverse gear and a ratio very well suited to motor vehicles having a high total spreading and favorable ratio ranges. They must also make a high starting ratio in forward direction and contain a direct gear possible, the same as is adequate for utilization in both passenger cars and in commercial vehicles. Besides, said transmission must have a low construction cost, especially require a small number of shifting elements and during sequential shifting mode prevent double shifts so that during gear shifts in defined gear groups only one shifting element be changed each time.
The problem on which this invention is based is to propose a multiple gear transmission of the kind mentioned above in which the construction cost is optimized and in addition the efficiency degree in the main drive gears is improved with regard to towing and gearing losses. Besides, in the inventive multiple gear transmission low torques act upon the shifting elements and planetary gear sets, the same as the rotational speeds of the shafts, shifting elements and planetary gear sets are kept as low as possible. In addition, the number of gears and the transmission spreading are increased so that seen or eight forward gears and at least one reverse gear can be advantageously implemented. The inventive transmission must also be fit for any design in a vehicle, especially for a front-transverse arrangement.